Merge pull request #99 from rjw57/fix-switch-backend

ensure preserve_backend_stack() preserves backend name

Author: rjw57

README.rst

@@ -73,6 +73,8 @@ Changes
 
 * Add queue parameter to low-level OpenCL ``colifilt`` and ``coldfilt`` functions.
 * Significantly increase speed of ``dtcwt.registration.estimatereg`` function.
+* Fix bug whereby ``dtcwt.backend_name`` was not restored when using
+  ``preserve_backend_stack``.
 
 0.9.1
 '''''

dtcwt/__init__.py

@@ -48,13 +48,15 @@ def _update_from_current_backend():
 
 class _BackendGuard(object):
     def __init__(self, stack):
+        # Explicitly copy the stack
         self._stack = list(stack)
 
     def __enter__(self):
         return _BACKEND_STACK
 
     def __exit__(self, exc_type, exc_value, exc_tb):
         dtcwt._BACKEND_STACK = self._stack
+        _update_from_current_backend()
         # only re-raise if it's *not* the exception that was
         # passed to throw(), because __exit__() must not raise
         # an exception unless __exit__() itself failed.  But

tests/testswitchbackends.py

@@ -80,11 +80,15 @@ def test_backend_with_guard_and_exception():
     correctly propagated.
 
     """
-    assert len(dtcwt._BACKEND_STACK) == 1
+    dtcwt.push_backend('numpy')
+    assert len(dtcwt._BACKEND_STACK) == 2
+    assert dtcwt.backend_name == 'numpy'
     def tst():
         with dtcwt.preserve_backend_stack():
-            dtcwt.push_backend('numpy')
-            assert len(dtcwt._BACKEND_STACK) == 2
+            dtcwt.push_backend('opencl')
+            assert dtcwt.backend_name == 'opencl'
+            assert len(dtcwt._BACKEND_STACK) == 3
             raise RuntimeError('test error')
     assert_raises(RuntimeError, tst)
-    assert len(dtcwt._BACKEND_STACK) == 1
+    assert dtcwt.backend_name == 'numpy'
+    assert len(dtcwt._BACKEND_STACK) == 2